This invention relates to an apparatus and system for treating waste water and sludge. More particularly, this invention relates to an apparatus and system for separating and drying floating components such as grease, fat, oil and/or solid components of an aqueous mixture, and for removing water from and drying sludge.
In many communities the local municipality provides a service of picking up waste water collected as an aqueous mixture of grease, fat, oil and/or solids pumped from grease traps of kitchen clean up areas of local restaurants. These grease traps are typically in the range of 500 to 1,000 gallons in size for providing a reasonable duration of time between emptying operations. This service prevents the dumping of this type of waste water directly into the public sewage system where the grease, fat, oil and/or solid components would likely create clogging of underground piping. A municipal vehicle such as a tank truck is sent around on a regular periodic or demand basis to drain these grease traps and return to the local waste water treatment facility to process the collected waste water.
The present apparatus would typically be located at a local waste water facility and would be incorporated into the conventional waste water treatment system at the facility. In addition, other components are added to the conventional waste water treatment system resulting in a new waste water treatment system in which the present apparatus is one of the components of the system. The present apparatus has been constructed to specifically handle and process waste water constituting an aqueous mixture containing grease, fat, oil and/or solid components collected from around the local community at places of generation of this type of waste water such as restaurants as discussed above. Further, the present apparatus and system have been devised to handle and process "scum" which is defined as a dirty aqueous mixture containing grease, fat, oil and/or solids generated at the upper surface portions of a primary tank or basin (settling pond), which is a typical component of a conventional waste water facility. The scum is typically removed from the upper surface portions of the primary basin by a surface skimmer, which collects and then transports the scum to another location of the facility for further treatment. In the present system, the scum would eventually be transported to the present apparatus for further treatment.
The system of the present invention is also devised to handle and process sludge collected at the bottom of the primary basin of the conventional waste water treatment facility. I the past, periodically the primary basins are drained of their liquid components for facilitating the removal of settled solids collected on their bottoms. These solids are then loaded into a digester where they are acted on by anaerobic bacteria resulting in the degradation of organic matter and the production of gases. A supernate and residual humus or stabilized digested sludge ar produced within the digester as a result of the bacteria action. The gas produced in the digester is predominantly methane, which at a few waste water treatment plants is used to operate generators and boilers. However, in the majority of plants the gas produced is not utilized, but instead is vented into he atmosphere and burned. The substantially clear water or supernate is drained and further treated at another location of the waste water treatment facility. The solids that have collected at the bottom of the digester in the form a sediment paste or digested humus are typically pumped to either a press or centrifuge to further remove water therefrom. The resulting waste mass from the press or centrifuge is typically loaded onto dump trucks for removal to dumps and landfill sites.
Due to greater public interest and concern with respect to difficulties and problems presented by dumps and landfills, such as seepage of waste into local water tables, policies and regulations have arisen that prevent or make difficult the dumping of this type of waste. Further, the waste removed from a press or centrifuge still contains a significant amount of water, with a moisture content of approximately seventy to eighty percent by weight, making it difficult to transport, handle and to compact at landfills because of its tendency to flow and to hydraulically pump under the weight of compaction equipment. Also, this type of waste has been known to dissolve back into solution by ground water when buried at dumps and landfills creating a significant seepage problem at the site.
The apparatus of the present invention is utilized to further process the separated scum from the separating chamber of the apparatus and the waste mass from a press or centrifuge by a drying process, resulting in dried waste mass. The dried waste mass substantially reduces the cost of transportation to dumps and landfills due to its greatly reduced weight, volume and its ability to be compacted. Further, the dried waste mass is more manageable for purposes of handling since it does not flow.
The dried waste mass is substantially more resistant to dissolving by ground water and can be readily compacted into a layer at a dump or landfill. When the waste mass or dried humus has been subjected to a drying process at a temperature in excess of 160.degree. F., with the attendant reduction of moisture content to under twenty-five (25) percent, all dangerous pathogens within the dried waste mass are destroyed. The dried waste mass is now sanitized to the point where it can be safely handled and applied to row crops as fertilizer or can be used for other agricultural purposes. The nitrogen content varies from 0.8 to 0.9 percent and the potassium and calcium contents are high. The EPA standards are met by the foregoing treatment. It is expected that the temperature within the drying oven will be in excess of 200.degree. F. and that the moisture content of the dried waste mass will be quite small. This will destroy all pathogenic bacteria and viruses, as well The addition of hydrated lime provides additional insurance that all pathogens will be destroyed due to the rise of the pH level to approximately 12. Further, the end product will be more friable and easy to apply to row crops. Thus, the present apparatus and system converts a substance that has previously been considered a problematical waste product into a useful product.
As described above, during operation of a conventional waste water treatment facility, methane gas is produced as a by-product of some of the treatment processes such as that occurring within a digester. The present apparatus and system utilize this methane gas as an energy source for fueling the drying chamber of the present apparatus. Thus, the cost involved in operating the present apparatus is minimal due to the essentially free energy source available at the waste water treatment facility.